Dirty Girl Motor Racing Article: Motorcycle tire information

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Motorcycle Tires

5 Questions you should be able to answer about your motorcycle tires

No trick questions, this is an open book test, you can check your tires to answer these 5 questions:
1) make and model of your tires
2) diameter of your rims
3) size of your tires
4) speed and load rating of your tires
5) date (week and year) of manufacture of your tires
If you can read the answers to all those questions on the sidewall of your tires, take a gold star and SKIP AHEAD. If you want to know how to find and read this information on your tires, read on.

The make and model of your tire is probably the least important information, probably only useful for bench racing, but very often that is the easiest to spot.

The diameter of your rims is probably something most riders know, and even if you know very little about your bike, it's a difficult thing to mix up - 16" tires simply won't fit on 17" rims, so it's not likely something that can get mixed up while your bike is in the shop.

The tire sidewall includes size information, usually now seen in metric (although there are inch designations and an alphabetic system too) which includes the width or section of the tire in millimeters, and the height of the tire as an aspect ratio (section height divided by section width multiplied by 100).

The speed and load rating of your tires are very likely to fall within a suitable range if the above criteria are met, but it's a good idea to check and make sure you'll be operating the tire within it's expected parameters.

Motorcycle tire markings and information

motorcycle tire information and how to read the sidewalls

For Road Racers: Dating your tires

We road racers do love our traction, don't we? Logically this translates to an appreciation of our tires, but dating your tires? Isn't that a bit extreme?

I'm not actually referring to (nor suggesting) a romantic liason with your rubber, but like a prospective date, you might want to know a little bit about your tires before comiting yourself.

For road racers who use DOT tires, the tire size markings are not much of a mystery, but 'metric' tire sizes sometimes perplex the vintage racer more accustomed to inches. The new bike I'm working on for next year has a 140/70-18 rear tire, which tells the experienced tire-marking-translator that I have an 18 inch rim (yes, that's the 'metric' tire size, go figure) with a tire that is 140 mm wide, and the height of the tire is 70% of it's 140mm width. So that simple looking numeric code is actually an inconvenient combination of metric, imperial and math.

Fitting the correctly sized tire for your rim is critical. An incorrectly sized tire will create the wrong shaped tire profile when mounted on your rim, which can have a disasterous effect on cornering traction.

Apart from size, tires carry a range of other markings, two of which are particularly important for racers, the speed rating and the date of manufacture.

There is actually a speed rating (A1) for tires that are rated to travel no more than 5 km/h, and since I can exceed that speed at a walking pace, I have trouble imagining what possible application a tire rating like that could have. Can anyone suggest what uses a tire like that might have? Anyway, tires on motorcycles usually have speed ratings like V (rated up to 240km/h) or Z (over 240km/h), but you might sometimes see H (rated for up to 210 km/h) or R (rated for up to 170 km/h). Except for H, you probably shouldn't see any letters from the first half of the alphabet in your tires speed rating.

The date code is possibly the most important tire marking to check before buying new tires. Tires, like milk, have a shelf life. Even with ideal storage tires, through a process called degassing, deteriorate over time. Unlike milk, tires do not come with a 'best before' date, but instead are labeled with their date of manufacture. Their birthdate if you will, although not exactly a birthday, since they are marked with week and year. The date of manufacture appears as a 4 digit numeric code, usually placed inside an oval area within the mold, which shows around the numbers on the tire. The first two digits of this code are the week, and the last two digits are the year (wwyy) so that a tire date code of 3808 would indicate tires made in the 38th week of 2008. Three number date codes were used prior to 2000, which are tires way WAY too old to be used for anything other than storage protection for rims. Since the shelf life of a tire is considered to be no more than 5 years, and due to the by-laws passed in the USA preventing the sale of motorcycle tires more than 5 years old, riders should be very leary of "deals" on tires until they check the mold date for themselves. A 5 year old tire isn't a deal, it's a rim-guard, it's dead, it would be pushing up the daisys if it weren't nailed to the perch.

For road racers on modern bikes, old tires are hardly ever a concern, they are going through many sets of tires each season, and buying tire sizes that sell in high volumes. For vintage road racers, old tires are more frequently a concern. The smaller displacement and lighter weight bikes don't consume tires as quickly, and some racers only change tires once a year (or less... yes, I eavesdrop in the tech line) Because we use less common tire sizes we are at greater risk of getting a tire that has been sitting around for a while too. When you buy your next set of tires make sure the mold date is 'fresh' and if you aren't sure when the tires that are on your bike now were made, it might be worthwhile to check now, while there's time to order new rubber over the winter.

CHECK YOUR TIRES FOR:

Your tire's birthday

This is probably the most critical and least known tire marking. This is a 4 digit number expressed as week and year (WWYY). Tires, like your helmet, are only good for 5 years, even under ideal circumstances. Modern tires contain volatile organic compounds that leach our over time in a process called de-gassing. Even tires stored in ideal conditions and never mounted on a rim are 'dead' after 5 years. Buying tires a few years old may not matter if you go through two sets of tires a season, but if your tires last you a few seasons, you won't want to mount an old tire.

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